Platelet activating factor (PAF). A possible direct mediator of anaphylaxis in the rabbit and a trigger for the vascular deposition of circulating immune complexes.

Evidence is presented that IgE-induced, basophil-derived, platelet-activating factor (PAF) causes sequestration of rabbit platelets during sublethal IgE-induced anaphylaxis, and produces a state of specific desensitization in the platelets upon their subsequent return to the circulation. Moreover, depletion of platelets from rabbits undergoing lethal anaphylaxis abrogated the mortality and markedly reduced other parameters of the anaphylaxis. It was suggested that PAF may represent a major mediator of this reaction. A number of lines of evidence have suggested in addition that PAF may play a role in acute experimental immune complex disen that PAF may play a role in acute experimental immune complex disease in rabbits by causing release of vasoactive amines from platelets, lase in rabbits by causing release of vasoactive amines from platelets, leading to increased vascular permeability and deposition of circulating immune complexes along filtering vascular membranes. This data, providing evidence for the action of PAF in vivo and implicating this action in two allergic reactions, supports the contention that PAF is an important mediator of acute allergic reactions.